The invention concerns a method for introducing a liquid sample into an NMR spectrometer to measure an NMR spectrum of the liquid sample, wherein the liquid sample is injected into a supply line and further liquids are subsequently supplied into the supply line that are separated from each other and from the liquid sample by gas bubbles.
A method of this type is disclosed in U.S. Pat. No. 5,397,989 A. In this conventional method, gas bubbles are generated between a sample liquid and a transport liquid in a sample loop to spatially separate the two liquids and prevent mixing thereof. The sample liquid and separating segments (gas and liquid segments) are sequentially drawn up into the sample loop using a needle. The sample loop is then connected to the NMR using a connecting capillary and can be pumped into the NMR spectrometer through that capillary. It is also possible to use an internal “parking” capillary which can be connected to the NMR using a valve, thereby also forming segments consisting of sample, gas and liquid segments, which are intermediately “parked” before being pumped towards the NMR spectrometer.
This method is disadvantageous in that the sample is held in a “parked” position until all gas and/or liquid segments have been drawn up into the sample loop. Only then are the sample with separating segments supplied to the NMR spectrometer. This method wastes substantial amounts of time which can deteriorate the measuring result, in particular, for instable samples. A further, much more serious problem is the so-called “back mixing” or “carry over”. Since only one needle is used for all operations, i.e. for drawing up the sample and also for drawing up the different liquid segments, the liquids in the storage containers may be contaminated and mixed within the capillaries. Such contamination can be prevented only through complex cleaning between the individual steps. This is possible only to a limited degree due to the danger that the cleaning agent diffuses into the needle and mixes with the drawn-up liquids.
It is the object of the invention to propose a method for supplying a liquid sample into an NMR spectrometer, which permits rapid sample transfer and prevents mixing and dilution of the individual segments.